A critical feature of rigid, magnetic data, disk storage devices is vulnerability to failure of the storage device as a result of the read/write transducing head slider wearing into the magnetic layer that is located on the disk's surface. Magnetic data storage improvements have been achieved by using a thin film magnetic coating, for example, in the range of about 25 nanometers thick, and by using a low head flying height, for example in the range of about 5 micro inches. Both of these factors require the tribology of the disk to be excellent in order for a useful lifetime to be achieved for the storage device. Generally, a thin film of lubricant molecules is required as part of the disk's tribological system. This lubricant film provides a low coefficient of friction when the head slider lands on the disk, for example as part of a start/stop operation, or when the head slider intermittently hits the disk while flying relative thereto.
As a result, the use of lubricants on the recording surface(s) of a magnetic recording disk is well known in the art. Generally, these lubricants are supplied as thin layers, for example from one to many monomolecular layers thick.
In the art of rigid, thin film memory disks, a lubricant is conventionally used to reduce friction, to prevent head stiction in the start/stop (S/S) area of the disk, and to provide a debris-free flying interface for the disk and its read/write transducing head.
Fluorocarbon lubricants are commonly used in a rotating rigid disk direct access storage device (DASD). These lubricants possess the desirable properties of chemical inertness, low surface tension, low volatility, and in addition these lubricants can be moisture repellant and can retard corrosion. However, these lubricants have a disadvantage in that they tend to centrifugally migrate to the outer edge of the disk, due to the force of disk rotation. This lubricant migration can lead to increased interference at the head/disk interface, and may eventually lead to complete failure of the interface.
The above mentioned related inventions describe disk lubrication systems wherein a reservoir contains a volatile organic lubricant. This volatile lubricant operates to continuously supply lubricant vapors to the recording surface of a magnetic recording disk.
Another approach to disk lubrication is to chemically bond a single, or simplex, layer of lubricant molecules to the disk's recording surface. In this case the lubricant is immobilized due to strong physical adsorption or weak pseudo-molecular bonding of the lubricant to the underlying disk surface. As a result, the lubricant does not appreciably evaporate from the recording surface over an extended period of use, nor does the lubricant gradually spin off of the disk surface as a function of the disk's high speed of rotation. Examples of such bonded lubricants are perfluoropolyethers (PFPE) having various hydrocarbon functional groups. The functional groups of these perfluoropolyether lubricants are active in bonding the lubricant molecules to the disk's recording surface. A sputtered carbon overcoat layer typically provides an active overcoat surface on the thin film magnetic layer, to which overcoat surface the lubricant is bonded. Other sputtered overcoat layers are also used. In this arrangement, after the lubricant is topically applied to the overcoat layer, the lubricant is bonded thereto by the application of heat, E-beam or by another source of irradiation that effects bonding of the lubricant molecules to the magnetic recording layer, or to the overcoat layer when one is used.
In this type of a bonded lubricant system, we have observed that the bonded lubricant layer usually does not provide uniform coverage of the disk's overcoat or thin film magnetic recording layer. Voids or thin areas tend to occur in the layer of bonded lubricant. This lack of integrity in the bonded lubricant layer may occur as a result of natural defects that occur during the bonding process or manufacturing process, or this lack of layer integrity may result from wear to the disk's surface during data processing.
Duplex layer, i.e. two layer, lubricant coatings on the magnetic recording layer of magnetic recording media is known in the art.
Such a duplex lubricant system can be formed subsequent to providing the above mentioned bonded lubricant layer, in which case it is customary to either leave the residual unbonded lubricant on the disk surface, to thereafter function as a second, mobile, lubricant layer, or the residual lubricant may be washed off after the bonding step, and a second unbonded lubricant layer may be topically applied, to thereby form a duplex lubricant coating on the disk. However, even such a duplex lubricant system is likely to develop nonuniform lubricant coverage (i.e. voids and/or thin areas).
The publication IEEE Transactions on Magnetics, Vol. MAG-23, No. 1, January 1987, at pages 33-35 describes the use of duplex fluorocarbon films, one film being chemically and permanently bonded to the media surface, and the other film being a lubricant that is overcoated onto the primed disk surface. The top lubricant is said to have the properties typical of a liquid lubricant.
UK Patent Application GB 2,155,810 A describes a magnetic recording medium comprising a non-magnetic substrate, a magnetic recording ferromagnetic film on one side of the substrate, and a topcoat layer formed on the surface of the recording layer, the topcoat layer comprising a radiation curable antioxidant and a lubricant.
U.S. Pat. No. 4,642,246 describes a process for lubricating a magnetic disk comprising contacting the disk with a functionalized lubricant having at least one functional terminal group, heating the lubricant so as to bond the functional terminal group to the surface of the disk, and then contacting the disk with a non-functionalized lubricant.
U.S. Pat. No. 4,713,287 describes a magnetic recording medium comprising a support having a thin magnetic film thereon, a thin layer of a fluorinated polymer on the magnetic film, and a lubricating agent coated on the polymer layer.
As stated previously, the above mentioned related inventions describe lubricant reservoir systems that operate to continuously supply lubricant vapors to magnetic recording disks by way of Langmuir adsorption kinetics.
While prior disk lubrication systems have been generally acceptable, as the data handling requirements of thin film magnetic recording disks increase, it is desirable that lubrication of the disks also be improved.